The field of the present invention pertains to drive mechanisms for providing intermittent rotary output. More specifically, the present invention concerns a piston-driven rack wherein a drive stroke of the rack intermittently rotates an output shaft, and wherein the angular driving motion of the output shaft may be preselected by an adjustment in the driving mechanism. The output shaft, for example, may be connected to a workpiece conveyor which is to be intermittently advanced in precisely uniform increments, and wherein the length of conveying motion must be adjustable to index workpieces on the conveyor to a processing station, or to change to other size workpieces.
A prior art drive system according to the outline above is disclosed in the Zwiebel U.S. Pat. No. 3,412,430 issued on November 26, 1968. The patentee disclosed a drive system including a reciprocable rack driving a pinion, and provides for adjustably setting the stroke of the rack without misaligned toothed elements in the system. In one embodiment of the invention disclosed in the patent, the toothed elements are a rack and pinion gear which are intermittently engaged. For this purpose, the rack has one end pivoted to a frame which is reciprocated by a fluid-operated cylinder. A toggle cylinder on the frame is connected to the rack and swings the rack into and out of engagement with the pinion. A second rack is positioned above the movable frame and is contacted by a bolt on the frame to limit the movement of the frame. This second rack has teeth at the same pitch as the first rack and is adjustably locked to a block also having the same pitch teeth. Thus, once the bolt and the second rack are properly adjusted, any relocation of the second rack to change the stroke of the first rack (via the movable frame) will assure that the first rack and its associated pinion will properly mesh when the toggle cylinder causes the rack to pivot against the pinion.